Hydrogen at extremely high pressures, upwards of a million times that
on the Earth's surface, can now be produced in physics laboratories.
Understanding hydrogen's behavior under such extreme conditions answers
questions about the interior of Jupiter, provides coveted information
on designing optimal fuel pellets for fusion energy, and yields information
on aging nuclear weapons without having to test them.
Reporting at the APS/AAS meeting in Albuquerque, two national labs
are producing seemingly contradictory high-pressure data on the universe's
most abundant element.
Using Sandia's Z machine, which runs tremendous amounts of electric
current to generate very high magnetic fields, researchers (Marcus Knudson,
505-845-7796, firstname.lastname@example.org) launch a metal plate that travels
at high speeds (up to 28 km/s, making it the fastest gun in the world)
towards a target containing low-temperature deuterium molecules (D2).
The impact of the plate launches a shock wave that compresses D2
to up to megabars of pressure. Deuterium, a neutron-containing isotope
of hydrogen, is used because its higher density enables it to be compressed
to much higher pressures than ordinary hydrogen.
The Livermore experiments, on the other hand, used the high-power (and
recently decommissioned) Nova laser to shock compress liquid D2.
The Livermore researchers (Robert Cauble, 925-422-1174, email@example.com)
find D2 to be much more compressible than do the Sandia researchers.
At a million atmospheres, for example, Livermore finds the D2
to be compressed by a factor of 6 while Sandia sees a compression of
a factor of 4.
If the Livermore results are correct, then there is more metallic hydrogen
in Jupiter's interior than previously thought and it is easier than
expected to trigger self-sustaining nuclear fusion in deuterium fuel
pellets, since they would be more compressible. If the Sandia results
are right, then more traditional assumptions hold.
But it's also possible, Cauble says, that both results are right (each
group's compression occurs in slightly different time scales). As a
final possibility, Cauble and Knudson admit, both results could be wrong
(they are both relatively new techniques).
These possibilities are being carefully explored in conjunction with
computer simulations of high-pressure hydrogen, which require the fastest
available computers in the world.
The question is likely to be settled with further experimental research,
including more data from Sandia and future laser experiments, possibly
occurring at Rochester's Omega facility.
The ultimate goal of these experiments is to determine hydrogen's equation
of state, the interrelationship between such properties as its pressure
and temperature, at these high-pressure conditions. Such information
can provide information on such things as the intriguing possibility
that gas-giant Jupiter has a solid-rock core.